ABCB7 and myelodysplastic syndrome with ring sideroblasts: No genomic abnormality in the ABCB7 gene was identified in our cases, suggesting that there could be a trans-acting factor responsible for the low levels of ABCB7 in RARS (analogous to the down regulation of the alpha-globin genes in the acquired HbH associated with MDS caused by mutations in the ATRX gene) [22].